Corrosion inhibitors



Patented Aug. 9, 1949 UNITED STATES PATENT CORROSION INHIBITORS John A Elder, Jr., Plainfield, N. J., assignor to Merck & 00., Inc., Rahway, N. J., a corporation of New Jersey No Drawing. Application November 30, 1945, Serial No. 632,119

6 Claims. 1

used include water and aqueous solutions containing at least one alcohol. The term alcohol as used in the specification and claims includes methanol, ethanol, propanol or other monohydroxy alcohols, and the polyhydroxy alcohols such as ethylene glycol, propylene glycol, diethylene glycol, and glycerine.

This invention has as an object the preparation of a new and useful corrosion inhibitor adapted to protect polymetallic systems Of iron, brass, copper, aluminum, solder and other metals in contact with liquids, such as liquid automotive cooling systems, heat exchangers, hot water systems, shock absorbers and hydraulic presses.

It is well known that water and aqueous alcoholic solutions exert a corrosive action on metals which results in the discoloration, roughening and pitting of the surface of the metals and the formation of corrosion products which either cling to the metals with consequent reduction of heat transfer efiiciency or slough oil and settle at points of low fluid velocity causing clogging of the system. Alkali metal salts of monochromates and dichromates have, for example, been tried to inhibit the corrosion of iron in contact with liquids. Sodium benzoate has been suggested for inhibiting the corrosion of zinc, iron and copper. It has been found, however, that these additions do not act or at least act to an insuilicient extent in polymetallic systems, for it is recognized that corrosion occurring in a polymetallic system is of an entirely difierent extent and character from that involving only one of the component metals.

I have found that the addition of a small amount of an alkali metal chromate. benzoic acid or an alkali metal salt thereof, and hexamethylene-tetramine to water or an aqueous alcoholic solution will prevent the corrosion of a polymetallic system, such as a system including two or more of the following metals: iron, aluminum, brass, copper, solder and other metals. It should be pointed out that my improved compositions may be utilized in automotive systems containing aluminum, such as aluminum or aluminum alloy engine heads, etc., as well as in those not containing aluminum or aluminum alloys. Either after the addition of these ingredients or simultaneously with them, sufliclent alkali is added 80 that the resultant solution has an operating pH of about 7.5-10.0. Alkali, as referred to above and hereinafter, includes alkali metal hydroxides and carbonates. It is presently found that adjusting the pH within the limits indicated above affords maximum corrosion inhibition, in various polymetallic systems. The quantity of alkali required is dependent upon the acidity of liquid medium :being'treated. The addition of these materials to water or an aqueous alcoholic solution in contact with a polymetallic system prevents the corrosion of all of the metals present even after heating a 65 C. for a year, as shown in Example 1.

only small quantities of ach material are necessary to provide a proper inhibiting action; con-' siderable variation in concentration of the inhibitor is permissible depending upon the contact liquid used, a suitable range by weight of the liquid is from about 0.20% to 1.00% of an alkali metal chromate, about 0.25% benzoic acid or an alkali metal salt thereof and 0.50% to 1.00% hexamethylene-tetramina,

It is to be further understood that the term, alkali metal chromates, as herein used includes such obvious chemical equivalents as alkali metal dichromates. For example, an alkali metal chromate can be formed in situ in the liquid medium by adding an alkali metal dichromate and an alkali. In this case one mole of the alkali metal dichromate reacts with two equivalents of alkali to produce two equivalents of the chromate. A corrosion inhibitor in which the components have been varied would consist, for example, of 0.20% to 1.00% sodium dichromate, 0.25% sodium benzoate and 0.50% to 1.00% hexamethylene-tetramine. An inhibitor in which benzoic acid had been substituted would be for example 0.20% to 1.00% sodium chromate, 0.25% benzoic acid and 0.50% to 1.00% hexamethylene-tetra- ,mine. An example of a mixture in which two components are substituted would be 0.20% to 1.00% sodium dichromate, 0.25% benzoic acid and 0.50% to 1.00% hexamethylene-tetramine. The pH of the solution of inhibitors shown previously is adjusted with alkali so that the operating pH of the inhibitor is about 7.5-100. All percentages are based on the metric volume of the aqueous system.

The following examples illustrate a method of carrying out the present invention, but it is to be understood that these examples are given by way of illustration and not of limitation.

v 3 Example I About 0.25% of sodium chromate, 0.25% of sodium 'benzoate and 1.0% of hexamethylenetetramine are added to tap water. (All percentages are on a weight per metric volume basis.) This aqueous solution was tested on a polymetallic system and under conditions actually encountered in automotive cooling systems. A piece of cast aluminum bolted to an overlapping piece of cast'iron wasmaifntained parallel to a small piece of copper; butt solderedtoasmaller piece of copper. The twoybran'chesWCre held.

about one halt-inch apart'jbyi copperwire which was steel boltedto the aluminum-branch and soldered to the copper'br'anch. Therewas limited access of air tothe I system. This apparatus was submerged in the contact'liquid which contained the inhibitor-to be tested. [The system was maintained at room ,temperature approximately ten hours a daywith no stirring and the remainder of. the timenthefsystem' was -maintained at 65C. and'mechanlcally stirred. Tests were continued for a period of one year. During this time there was substantially no indication of corrosion of any of the metals and substantlally no sludge formation.

Example II About 0.20% of sodium dichromate dihydrate, 0.15% of sodium carbonate monohydrate, 0.25% of sodium benzoate and 1.0% of hexamethylenetetramine are added to tapwater. This solution was subjectedto th same test conditions as used in Example I for six months at which time substantially no corrosion of the metals was noted.

Example III About 0.25% of sodium chromate, 0.25% sodium benzoate and 1.00% of hexamethylene-tetramine are added to an aqueous solution of half ethanol and half tap water by volume. The test described in Example I was continued for one year with substantially no indication of corrosion i of the metals present.

Example IV About 0.25% of sodium chromate; 0.25% sodium benzoate and 1.00% of hexamethylene-tet-.

ramine are added to an aqueous solution of half ethylene glycol and half tap water by volume. T his solution was subjected to the'same test con-. ditions as used in Example I for ten months at which time substantially no corrosion of the metals was observed.

Example About ms. (0.2%) of sodium dichromate dihydrate, 23 gms. (0.15%) sodium carbonate monohydrate, 38 gms. (0.25%) sodium benzoate and '75 gms. (0.5%) hexamethylene-tetramine were added to a clean 16 quart automotive cooling system containing tap water. After 3 months the coolant was drained and inhibitor found not to be depleted. Then about 46 gms. (0.3%) sodium dichromate dihydrate, 34 gms. (0.22%) sodium carbonate monohydrate, 38 gms. (0.25%) sodium benzoate and '75 gms. (0.5%) hexamethylenetetramine were added to the same cooling system containing 4 quarts of ethylene glycol in a total of 16 quarts of coolant. After 8 months the inhibitor was not depleted and examination of the engine head and block, the radiator and the drained coolant showed no indication of corrosion. Furthermore, the rubber hose connections from engine to radiator and car heater were not injured by contact with the solution.

The mixture described in this invention inhibit corrosion to an extent impossible with any one of the components alone or any binary combination of them. Corrosion tests were made with sodium chromate alone, with sodium chromate and sodium benzoate and with sodium chromate and hexamethylene-tetramine dissolved in tap water and tested in the polymetallic system described in Example I.

Results f I these experiments are tabulated below:

Inhibitor Results Corrosion of edges of aluminum and etching of copper.

' alumi- 25% sodium chromate (aqueous). .25% sodium chromate aqueous... }Corrcsion of iron and 25% sodium benzoate nun 25% sodium chromate aqueous. }Alu m11ium ad acent to H011 hexamethylene-tetramine.. pitted.

Modifications may be made in carrying out the present invention without departing from the spirit and scope thereof and the inventionis to be limited only by the appended claims.

I claim:

1. The process of inhibiting the corrosion oi metals in polymetallic systems when said metals are in contact with an aqueous system, selected from the class consisting of water and aqueous alcohol which comprises adding to said aqueous system a corrosion inhibitor which comprises: a chromium containing salt selected from the group which consists of the alkali metal chromates and a mixture of the alkali metal dichromates and the alkali metal carbonates in amounts ranging from 0.20%to 1.00%; an organic compound selected from the group which consists of benzoic acid and salts of benzoic acid in amounts ranging from 0.10% to 0.25%; and hexamethylenetetramine in amountsranging from 0.50% to 1.00%, said percentages being based on the metric volume of said aqueous system, and being selected to provide a pH of about 7.5 to 10.0 in the aqueous system.

2. The process of inhibiting the corrosion of metals in polymetallic systems when said metals are in contact with'an aqueous system selected from the class consisting of water and aqueous alcohol which comprises adding to said system a corrosion inhibitor which comprises an alkali metal chromate in amounts ranging from 0.20% to 1.00%, salts of benzoic acid in amounts ranging from 0.10% to 0.25%; and hexamethylenetetramine in amounts ranging from 0.50% to 1.00%, said percentages being based on the metric volume of said aqueous system and being selected to provide a pH of about 7.5 to 10.0 in the aqueous system.

3. The process of inhibiting the corrosion of metals in polymetallic systems when said metals are in contact with an aqueous system selected from the class consisting of water and aqueous alcohol which comprises adding to said aqueous system a corrosion inhibitor which comprises:

0.25% of sodium chromate, 0.25% sodium benzoate and 1.00% hexamethylenetetramine, said percentages being based on the metric volume of said aqueous system.

4. A' non-corrosive liquid which consists of an aqueous system selected from the class consisting of water and aqueous alcohol and a corrosion inhibitor therefor which consists of: a chromium containing salt selected from the group which consists of the alkali metal chromates, and a mixture of the alkali metal dichromates and the alkali metal carbonates in amounts ranging from 0.20% to 1.00%: an organic compound selected from the group which consists of benzoic acid and salts of benzoic acid in amounts ranging from 0.10% to 0.25% and hexamethylenetetramine in amounts ranging from 0.50% to 1.00%, said percentages being based on the metric volume of said aqueous system, and being selected to provide a pH of about 7.5 to 10.0 in the aqueous system.

5. A non-corrosive liquid which consists of an aqueous system selected from the class consisting of water and aqueous alcohol, and a corrosion inhibitor therefor which consists of: an alkali metal chromate in amounts rangin from 0.20% to 1.00%; a salt of benzoic acid in amounts ranging from 0.10% to 0.25%, and hexamethylene- 6 tetramine in amounts ranging from 0.50% to 1.00%, said percentages being based on the metric volume of said aqueous system, and being selected to provide a pH of about 7.5 to 10.0 in the aqueous system.

6. A non-corrosive liquid which consists of an aqueous system selected from the class consisting of water and aqueous alcohol and a corrosion inhibitor therefor which consists of: 25% sodium chromate; '25% sodium benzoate, and 1.00% hexamethylenetetramine, said percentages being based on the metric volume of said aqueous system.

JOHN A. ELDER, Ja.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

